PARASITIC COPEPODS—CALIGIDJE— WILSON. 



539 



the adult stage is never found on the outside surface of the body or 

 on the fins, but (hose are the very places most easily accessible to the 

 young metanauplius and where consequently it must be sought. 



And then the larva 1 are so small as almost to require a hand lens for 

 recognition, and their color is so similar to that of the fish's body as to 

 afford them ample protection. 



About the only way to detect them in most cases is to take the fish 

 directly from the water, and while it still retains a film of water over 

 the entire outside of the body hold it up to the light in such a way as 

 to get the rays reflected from the surface. The larva, being attached 

 loosely, stands oil' from the surface and breaks the reflection. If the 



Fin. :>s. — N.vri'urs of Caliuus hoxito nearly ready to moult into a metanauplius. The 



PIGMENT, WHICH AT FIRST WAS IN A CONTINUOUS RING, IS NOW BROKEN UP. VENTRAL VIEW, 

 SHGH !M. l.A BE1 M. 



fish has been dropped to the ground or into the bottom of a boat there 

 is very little use to search it for development material. 



In view of these difficulties it is not surprising that so few larval 

 stages have been secured hitherto, or that investigators overlooked all 

 luit the largest and most advanced embryos. 



As has been stated the nauplius at first is entirely unsegmented, with 

 the three pairs of appendages grouped around the mouth near the 

 anterior end of the body. The first moult occurs during the first 

 thirty-six hours, usually in the night: the nauplius emerges with its 

 body considerably elongated and with the evident beginnings of seg- 

 mentation posteriorly. The division between head and thorax is 

 plainly indicated in the clear edge which borders the carapace (tig. 37). 



